1. Field of the Invention
The present invention relates to an optical pickup and a recording and/or reproducing apparatus focusing a laser beam on an optical disk.
2. Description of the Related Art
FIG. 1 is a view of the configuration of an optical pickup of the related art.
This optical pickup 1 has a semiconductor laser 4, a collimator lens 5, a beam splitter 3, an objective lens 2, a focus lens 6, a cylindrical lens 7, and a photo detector 8.
The semiconductor laser 4 outputs a linear polarized laser beam and supplies the same to the collimator lens 5.
The collimator lens 5 collimates the laser beam from the semiconductor laser 4 to a parallel beam and supplies the same to the beam splitter 3.
The beam splitter 3 passes the laser beam from the collimator lens 5 therethrough and supplies it to the objective lens 2.
The objective lens 2 condenses the laser beam from the beam splitter 3 and supplies it to a track of an optical disk 80.
Further, the objective lens 2 returns the laser beam reflected at the optical disk 80 to the beam splitter 3.
The beam splitter 3 receives the laser beam from the optical disk 2 and reflects the incident laser beam and supplies it to the focus lens 6.
The focus lens 6 focuses the laser beam from the beam splitter 3 and supplies it to the cylindrical lens 7.
The cylindrical lens 7 passes the laser beam from the focus lens 6 and supplies it to the photo detector 8.
The photo detector 8 receives the laser beam from the cylindrical lens 7 at its light receiving portion and generates an output signal.
FIG. 2 is an explanatory diagram of the configuration of the light receiving portion of the photo detector 8.
The photo detector 8 is a four-divided photo detector obtained by equally dividing a light receiving portion 8S to four by two division lines 8Sx and 8Sy.
The light receiving portion 8S has four divided regions 8A to 8D. In the light receiving portion 8S of FIG. 2, a beam spot MS is formed by the laser beam from the cylindrical lens 7.
The direction of the generatrix of the cylindrical lens 7 forms an angle of about 45 degrees or about 135 degrees with respect to the direction of the division line 8Sx or division line 8Sy of the light receiving portion 8S.
The intersecting point of the division lines 8Sx and 8Sy is located at the center or substantially the center of the laser beam passing through the cylindrical lens 7.
The shape of the beam spot MS formed at the light receiving portion 8S changes in a diagonal direction in accordance with the distance between the optical disk 80 and the objective lens 2, so it is possible to detect focus deviation at the optical disk 80 by an astigmatism method based on output signals generated by the divided regions 8A to 8D.
A focus error signal FE is expressed by the following equation (1) by using output signals SA to SD generated by the divided regions 8A to 8D.
FE=SA+SCxe2x88x92(SB+SD)xe2x80x83xe2x80x83(1)
Summarizing the problem to be solved by the invention, in an optical disk of a structure having lands and grooves, the focus error signal FE becomes a different value depending on whether the position of the focus is on a land or is in a groove. This will be explained by referring to FIG. 3.
FIG. 3 is a graph showing various focus error signals with respect to the lands and the grooves. A focus error signal in the case where the track is a land is indicated by a dotted line LA, while a focus error signal in the case where the track is a groove is indicated by a dotted line GR.
The curves LA and GR of the focus error signals shown in FIG. 3 are expressed as values of percentage (100xc3x97FE/xcexa3) obtained by standardizing (normalizing) the value obtained by equation (1) by a sum xcexa3 (=SA+SB+SC+SD) of the output signals SA to SD for convenience. Further, the relative distance from the focus position (focused position) where the laser beam from the objective lens is condensed to a recording surface of the optical disk is defined as an amount of defocus.
In a mirror disk, an optical disk of a structure with no grooves, when the recording surface is located at the focused position, the value of the focus error signal becomes 0.
In an optical disk having a land and groove structure, however, when the recording surface of the optical disk is located at the focused position and the beam is focused (where the amount of defocus is 0), the value of the focus error signal does not become 0. This is because diffraction of light due to the lands and/or grooves occurs when the laser beam is reflected at the track, interference of the light occurs at the light receiving portion of the photo detector, and an offset occurs in the focus error signal at the time of focusing.
Further, when the ratio of the widths of the lands and the grooves, the depth of the grooves, etc. differ due to the differences of the optical disks, the value of the detection error in focus detection at the focused position changes. Namely, accurate detection of the focus error has been difficult in the method of the related art not only in optical disks of the land and groove structure, but in all optical disks having any groove widths and depths.
An object of the present invention is to provide an optical pickup and a recording and/or reproducing apparatus capable of preventing interference of light in a photo detector.
A laser beam reflected at a track of an optical disk having land and/or grooves includes 0-th order diffraction light and +1st order diffraction light created due to the diffraction by the lands and/or grooves.
It can be considered that, by passing this laser beam containing the 0-th order diffraction light and the +1st order diffraction light through a cylindrical lens and supplying this to the photo detector, interference of light occurs between a region in which the 0-th order diffraction light and the +1st order diffraction light overlap and a region in which they do not overlap, beam spots of the light receiving portion form an asymmetric intensity distribution with respect to the division lines at the time of focus, and therefore the focus error signal does not become 0 at the time of focus as shown in FIG. 3 described above.
FIG. 4 is an explanatory view of the state of the laser beam (returned laser beam) reflected at the beam splitter 3 and supplied to the focus lens 6 in the optical pickup 1 of FIG. 1, in which a contour of the 0-th order diffraction light is indicated by a solid line ring, and the contour of the +1st order diffraction light is indicated by a broken line ring.
A distance d0 up to the center of the +1st order diffraction light with respect to the center of the 0-th order diffraction light is expressed by the following equation (2) by a pitch p in a radius direction of the groove, a wavelength xcex of the laser beam, and a numerical aperture NA of the objective lens 2:
d0=(xcex/NA)/pxe2x80x83xe2x80x83(2)
Here, the radius of the 0-th order diffraction light determined by the radius of the objective lens 2 was standardized (normalized) and defined as 1. The radius of this 0-th order diffraction light is equal to the radius of the +1st order diffraction light and corresponds to the radius (or aperture) of the objective lens 2.
In the explanatory diagram of FIG. 4, the case where d0=1, that is the case where xcex/NA=p, is exemplified, and the contours of the +1st order diffraction light contact each other. If parameters such as the wavelength xcex, numerical aperture NA, and the pitch p are determined, the region in which the 0-th order diffraction light and the +1st order diffraction light overlap (overlapping region) and the region where they do not overlap (nonoverlapping region) are uniquely determined.
In the optical pickup and the recording and/or reproducing apparatus according to the present invention, the overlapping region where the 0-th order diffraction light and the +1st order diffraction light from the optical disk 80 overlap and the nonoverlapping region are made mutually intersecting linear polarized light or substantially mutually intersecting linear polarized light.
By making the polarization directions of laser beams of the overlapping region and the nonoverlapping region perpendicularly intersect, the interference of the light at the light receiving portion of the photo detector can be suppressed, the focus error signal can be made to match between the case where the laser beam is focused and supplied to a land and the case where it is supplied to a groove and it is possible to make the focus error signal 0 at the time of focus. For example, as shown in the explanatory view of FIG. 5, the focus error signal can be made to match between the case where the focus of the laser beam is located on a land and the case where it is located in a groove and it is possible to make the focus error signal 0 at the time of focus.
Further, in another optical pickup and recording and/or reproducing apparatus according to the present invention, either of a laser beam in the overlapping region of the 0-th order diffraction light and the +1st order diffraction light and a laser beam in the nonoverlapping region is blocked.
By blocking one of the laser beams in the overlapping region and the nonoverlapping region, the interference of light in the light receiving portion of the photo detector can be eliminated, the focus error signal can be made to match between the case where the laser beam is condense and supplied to a land and the case where it is supplied to a groove, and it is possible to make the focus error signal 0 at the time of focus. For example, as shown in the graph of FIG. 5, the focus error signal can be made to match between the case where the focus of the laser beam is located on a land and the case where it is located in a groove, and it is possible to make the focus error signal 0 at the time of focus.
Below, the configurations of the optical pickup and the recording and/or reproducing apparatus according to the present invention will be described.
According to a first aspect of the present invention, there is provided an optical pickup comprising a laser for outputting a linear polarized laser beam, an objective lens for condensing a laser beam from the laser and supplying it to a track of an optical disk with lands and/or grooves formed therein, a polarization plate supplied with the laser beam reflected at the optical disk via the objective lens and polarizing an overlapping region in which a 0-th order diffraction light and a 1st order diffraction light contained in the supplied laser beam overlap and a nonoverlapping region to linear polarized light orthogonal or substantially orthogonal to each other, and a photo detector supplied with the laser beam passed through the polarization plate.
Preferably, further provision is made of a cylindrical lens supplied with the laser beam passed through the polarization plate, the photo detector has a light receiving portion for receiving the laser beam passed through the cylindrical lens, the related light receiving portion is equally divided to four or substantially equally divided to four by two orthogonal division lines, an intersecting point of the two division lines is arranged at the center or substantially the center of the laser beam passed through the cylindrical lens, and a direction of a division line and a direction of a generatrix of the cylindrical lens form an angle of about 45 degrees or about 135 degrees.
Alternatively, further provision is further made of a collimator lens for collimating the laser beam output from the laser to a parallel beam and a beam splitter supplied with the laser beam as a parallel beam from the collimator lens, the objective lens condenses the laser beam passed through the beam splitter, supplies the same to the optical disk, and returns the laser beam reflected at the optical disk to the beam splitter, and the beam splitter supplies the laser beam from the objective lens to the polarization plate.
According to a second aspect of the present invention, there is provided an optical pickup having a laser for outputting a linear polarized laser beam, an objective lens for condensing a laser beam from the laser and supplying the same to a track of an optical disk with lands and/or grooves formed therein, a Wollaston polarizing prism which is supplied with the laser beam reflected at the optical disk via the objective lens and separates the supplied laser beam to a main laser beam and first and second sub laser beams, a polarization plate supplied with the laser beams passed through the Wollaston polarizing prism and polarizing an overlapping region in which a 0-th order diffraction light and a 1st order diffraction light contained in the main laser beam among the supplied laser beams overlap and a nonoverlapping region to linear polarized light orthogonal or substantially orthogonal to each other, and a photo detector supplied with the laser beam passed through the polarization plate.
Preferably, further provision is made of a cylindrical lens supplied with the laser beam passed through the polarization plate, the photo detector has a main light receiving portion for receiving the main laser beam passed through the cylindrical lens, a first sub light receiving portion for receiving the first sub laser beam passed through the cylindrical lens, and a second sub light receiving portion for receiving the second sub laser beam passed through the cylindrical lens, the main light receiving portion is equally divided to four or substantially equally divided to four by two orthogonal division lines, an intersecting point of the two division lines is arranged at the center or substantially the center of the main laser beam passed through the cylindrical lens, a direction of a division line and a direction of a generatrix of the cylindrical lens form an angle of about 45 degrees or about 135 degrees, and the optical disk is a magneto-optical disk.
Alternatively, further provision is made of a collimator lens for collimating the laser beam output from the laser to a parallel beam and a beam splitter supplied with the laser beam as a parallel beam from the collimator lens, the objective lens condenses the laser beam passed through the beam splitter, supplies the same to the optical disk, and returns the laser beam reflected at the optical disk to the beam splitter, and the beam splitter supplies the laser beam from the objective lens to the Wollaston polarizing prism.
According to a third aspect of the present invention, there is provided an optical pickup having a laser for outputting a linear polarized laser beam, an objective lens for condensing a laser beam from the laser and supplying the same to a track of an optical disk with lands and/or grooves formed therein, a Wollaston polarizing prism which is supplied with the laser beam reflected at the optical disk via the objective lens and separates the supplied laser beam to a main laser beam and first and second sub laser beams, a substrate supplied with the laser beams passed through the Wollaston polarizing prism and allowing either of the laser beam in the overlapping region in which the 0-th order diffraction light and the 1st order diffraction light contained in the main laser beam among the supplied laser beams overlap and the laser beam in the nonoverlapping region in which they do not overlap to pass therethrough but blocking the other, and a photo detector supplied with the laser beam passed through the polarization plate.
Preferably, further provision is made of a cylindrical lens supplied with the laser beam passed through the substrate, the photo detector has a main light receiving portion for receiving the main laser beam passed through the cylindrical lens, a first sub light receiving portion for receiving the first sub laser beam passed through the cylindrical lens, and a second sub light receiving portion for receiving the second sub laser beam passed through the cylindrical lens, the main light receiving portion is equally divided to four or substantially equally divided to four by two orthogonal division lines, an intersecting point of the two division lines is arranged at the center or substantially the center of the main laser beam passed through the cylindrical lens, a direction of a division line and a direction of a generatrix of the cylindrical lens form an angle of about 45 degrees or about 135 degrees, and the optical disk is a magneto-optical disk.
Alternatively, further provision is made of a collimator lens for collimating the laser beam output from the laser to a parallel beam and a beam splitter supplied with the laser beam as a parallel beam from the collimator lens, the objective lens condenses the laser beam passed through the beam splitter, supplies the same to the optical disk, and returns the laser beam reflected at the optical disk to the beam splitter, and the beam splitter supplies the laser beam from the objective lens to the Wollaston polarizing prism.
According to a fourth aspect of the present invention, there is provided an optical pickup having a laser for outputting a linear polarized laser beam, an objective lens for condensing a laser beam from the laser and supplying the same to a track of an optical disk with lands and/or grooves formed therein, a substrate supplied with the laser beam reflected at the optical disk via the objective lens and allowing one of the laser beam in the overlapping region in which the 0-th order diffraction light and the 1st order diffraction light contained in the supplied laser beam overlap and the laser beam in the nonoverlapping region in which they do not overlap to pass therethrough but blocking the other, and a photo detector supplied with the laser beam passed through the substrate.
Preferably, further provision is made of a cylindrical lens supplied with the laser beam passed through the substrate, the photo detector has a light receiving portion for receiving the laser beam passed through the cylindrical lens, the related light receiving portion is equally divided to four or substantially equally divided to four by two orthogonal division lines, an intersecting point of the two division lines is arranged at the center or substantially the center of the laser beam passed through the cylindrical lens, and a direction of a the division line and a direction of a generatrix of the cylindrical lens form an angle of about 45 degrees or about 135 degrees.
Alternatively, further provision is made of a collimator lens for collimating the laser beam output from the laser to a parallel beam and a beam splitter supplied with the laser beam as a parallel beam from the collimator lens, the objective lens condenses the laser beam passed through the beam splitter, supplies the same to the optical disk, and returns the laser beam reflected at the optical disk to the beam splitter, and the beam splitter supplies the laser beam from the objective lens to the substrate.
According to a fifth aspect of the present invention, there is provided a first recording and/or reproducing apparatus having a laser for outputting a linear polarized laser beam, an objective lens for condensing a laser beam from the laser and supplying the same to a track of an optical disk with lands and/or grooves formed therein, a polarization plate supplied with the laser beam reflected at the optical disk via the objective lens and polarizing an overlapping region in which a 0-th order diffraction light and a 1st order diffraction light contained in the supplied laser beam overlap and a nonoverlapping region to linear polarized light orthogonal or substantially orthogonal to each other, a photo detector supplied with the laser beam passed through the polarization plate, a generation circuit for generating a focus error signal and a reproduction signal based on an output signal of the photo detector, a detection circuit for detecting recorded information of the optical disk based on the reproduction signal, and an actuator for moving the objective lens in a focus direction vertical to the recording surface of the optical disk based on the focus error signal.
More preferably, further provision is made of a cylindrical lens supplied with the laser beam passed through the polarization plate, the photo detector has a light receiving portion for receiving the laser beam passed through the cylindrical lens, the related light receiving portion is equally divided to four or substantially equally divided to four by two orthogonal division lines, an intersecting point of the two division lines is arranged at the center or substantially the center of the laser beam passed through the cylindrical lens, a direction of a division line and a direction of a generatrix of the cylindrical lens form an angle of about 45 degrees or about 135 degrees, and the generation circuit generates the focus error signal based on a difference between a sum of output signals of two divided regions located in one diagonal direction among four divided regions obtained by dividing the light receiving portion and a sum of the output signals of two divided regions located in the other diagonal direction and generates the reproduction signal based on a sum of the output signals of the four divided regions.
Still more preferably, further provision is made of a collimator lens for collimating the laser beam output from the laser to a parallel beam and a beam splitter supplied with the laser beam as a parallel beam from the collimator lens, the objective lens condenses the laser beams passed through the beam splitter, supplies the same to the optical disk, and returns the laser beam reflected at the optical disk to the beam splitter, and the beam splitter supplies the laser beam from the objective lens to the polarization plate.
According to a sixth aspect of the present invention, there is provided a laser for outputting a linear polarized laser beam, an objective lens for condensing a laser beam from the laser and supplying the same to a track of an optical disk with lands and/or grooves formed therein, a Wollaston polarizing prism which is supplied with the laser beam reflected at the optical disk via the objective lens and separates the supplied laser beam to a main laser beam and first and second sub laser beams, a polarization plate supplied with the laser beams passed through the Wollaston polarizing prism and changing an overlapping region in which a 0-th order diffraction light and a 1st order diffraction light contained in the main laser beam among the supplied laser beams overlap and a nonoverlapplng region to linear polarized light orthogonal or substantially orthogonal to each other, a photo detector supplied with the laser beam passed through the polarization plate, a generation circuit for generating a focus error signal and a reproduction signal based on an output signal of the photo detector, a detection circuit for detecting recorded information of the optical disk based on the reproduction signal, and an actuator for moving the objective lens in a focus direction vertical to the recording surface of the optical disk based on the focus error signal.
Preferably, further provision is made of a cylindrical lens supplied with the laser beam passed through the polarization plate, the photo detector has a main light receiving portion for receiving the main laser beam passed through the cylindrical lens, a first sub light receiving portion for receiving the first sub laser beam passed through the cylindrical lens, and a second sub light receiving portion for receiving the second sub laser beam passed through the cylindrical lens, the main light receiving portion is equally divided to four or substantially equally divided to four by two orthogonal division lines, an intersecting point of the two division lines is arranged at the center or substantially the center of the main laser beam passed through the cylindrical lens, a direction of a division line and a direction of a generatrix of the cylindrical lens form an angle of about 45 degrees or about 135 degrees, the optical disk is a magneto-optical disk, and the generation circuit generates the focus error signal based on a difference between a sum of output signals of two divided regions located in one diagonal direction among four divided regions obtained by dividing the light receiving portion and a sum of the output signals of two divided regions located in the other diagonal direction and generates the reproduction signal based on a difference between the output signals of the first and second sub light receiving portions.
Alternatively, further provision is made of a collimator lens for collimating the laser beam output from the laser to a parallel beam and a beam splitter supplied with the laser beam as a parallel beam from the collimator lens, the objective lens condenses the laser beam passed through the beam splitter, supplies the same to the optical disk, and returns the laser beam reflected at the optical disk to the, beam splitter, and the beam splitter supplies the laser beam from the objective lens to the Wollaston polarizing prism.
According to a seventh aspect of the present invention, there is provided a recording and/or reproducing apparatus having a laser for outputting a linear polarized laser beam, an objective lens for condensing a laser beam from the laser and supplying the same to a track of an optical disk with lands and/or grooves formed therein, a Wollaston polarizing prism which is supplied with the laser beam reflected at the optical disk via the objective lens and separates the supplied laser beam to a main laser beam and first and second sub laser beams, a substrate supplied with the laser beam passed through the Wollaston polarizing prism and allowing one of the laser beam in the overlapping region in which the 0-th order diffraction light and the 1st order diffraction light contained in the main laser beam among the supplied laser beams overlap and the laser beam in the nonoverlapping region in which they do not overlap to pass therethrough, but blocking the other, a photo detector supplied with the laser beam passed through the polarization plate, a generation circuit for generating a focus error signal and a reproduction signal based on an output signal of the photo detector, a detection circuit for detecting recorded information of the optical disk based on the reproduction signal, and an actuator for moving the objective lens in a focus direction vertical to the recording surface of the optical disk based on the focus error signal.
More preferably, further provision is made of a cylindrical lens supplied with the laser beam passed through the substrate, the photo detector has a main light receiving portion for receiving the main laser beam passed through the cylindrical lens, a first sub light receiving portion for receiving the first sub laser beam passed through the cylindrical lens, and a second sub light receiving portion for receiving the second sub laser beam passed through the cylindrical lens, the main light receiving portion is equally divided to four or substantially equally divided to four by two orthogonal division lines, an intersecting point of the two division lines is arranged at the center or substantially the center of the main laser beam passed through the cylindrical lens, a direction of a division line and a direction of a generatrix of the cylindrical lens form an angle of about 45 degrees or about 135 degrees, the optical disk is a magneto-optical disk, and the generation circuit generates the focus error signal based on a difference between a sum of output signals of two divided regions located in one diagonal direction among four divided regions obtained by dividing the light receiving portion and a sum of the output signals of two divided regions located in the other diagonal direction and generates the reproduction signal based on a difference between the output signals of the first and second sub light receiving portions.
Alternatively, further provision is made of a collimator lens for collimating the laser beam output from the laser to a parallel beam and a beam splitter supplied with the laser beam as a parallel beam from the collimator lens, the objective lens condenses the laser beams passed through the beam splitter, supplies the same to the optical disk, and returns the laser beam reflected at the optical disk to the beam splitter, and the beam splitter supplies the laser beam from the objective lens to the Wollaston polarizing prism.
According to an eighth aspect of the present invention, there is provided a recording and/or reproducing apparatus having a laser for outputting a linear polarized laser beam, an objective lens for condensing a laser beam from the laser and supplying the same to a track of an optical disk with lands and/or grooves formed therein, a substrate supplied with the laser beam reflected at the optical disk via the objective lens and allowing one of the laser beam in the overlapping region in which the 0-th order diffraction light and the 1st order diffraction light contained in the supplied laser beam overlap and the laser beam in the nonoverlapping region in which they do not overlap to pass therethrough but blocking the other, a photo detector supplied with a laser beam passed through the substrate, a generation circuit for generating a focus error signal and a reproduction signal based on an output signal of the photo detector, a detection circuit for detecting recorded information of the optical disk based on the reproduction signal, and an actuator for moving the objective lens in a focus direction vertical to the recording surface of the optical disk based on the focus error signal.
Preferably, further provision is made of a cylindrical lens supplied with the laser beam passed through the substrate, the photo detector has a light receiving portion for receiving the laser beam passed through the cylindrical lens, the related light receiving portion is equally divided to four or substantially equally divided to four by two orthogonal division lines, an intersecting point of the two division lines is arranged at the center or substantially the center of the laser beam passed through the cylindrical lens, and a direction of a division line and a direction of a generatrix of the cylindrical lens form an angle of about 45 degrees or about 135 degrees, the generation circuit generates the focus error signal based on a difference between a sum of output signals of two divided regions located in one diagonal direction among four divided regions obtained by dividing the light receiving portion and a sum of the output signals of two divided regions located in the other diagonal direction and generates the reproduction signal based on a sum of the output signals of the four divided regions.
Alternatively, further provision is made of a collimator lens for collimating the laser beam output from the laser to a parallel beam and a beam splitter supplied with the laser beam as a parallel beam from the collimator lens, the objective lens condenses the laser beams passed through the beam splitter, supplies the same to the optical disk, and returns the laser beam reflected at the optical disk to the beam splitter, and the beam splitter supplies the laser beam from the objective lens to the substrate.